Social media protests have their limits, but one thing they're very, very good at is grassroots media criticism.

The injury, a deadly one, came first. Unarmed 18-year-old Michael Brown was shot to death by police in Ferguson, Mo. Then came the insult: many news accounts used a photo of Brown that showed him, unsmiling, gesturing at the camera in a way that led to unsubstantiated claims that he was “flashing gang signs.”